The invention relates generally to a new nonwoven material which, when employed as surface voile or sheet or as a supplement to the surface voile as strip in the crotch region in an absorbent article of hygiene such as a diaper or dressing for the incontinent, allows better isolation of the user""s skin from the absorbent part of the article of hygiene. In particular, this new material is favorable to the time taken by the body fluids to pass through and to resistance to rewetting, and does not become fluffy.
In general, absorbent articles of hygiene, such as diapers and dressings for the incontinent, comprise an outer layer of liquid-impervious material, a pad made of absorbent material and a surface voile or sheet which is permeable to body fluids such as urine, of size and shave which are similar to those of the impervious outer layer of the article. The purpose of this surface voile which is permeable to body fluids is to isolate the skin from the moistened absorbent pad. Consequently, the surface voile must have an appropriate degree of softness and provide the required isolation between the skin and the absorbent pad. The purpose of the absorbent pad is to absorb the fluids and consequently it must have a high rate of absorption and a high absorbency. A particularly effective absorbent pad is described in document EP-A-0,232,729. This absorbent pad or mat is made up of a sheet of long absorbent fibers, the faces of said sheet being lined with a layer of cellulose wadding. The sheet lined with the layers of wadding is needled from both sides.
In the absorbent articles of hygiene absorbent mats or pads are covered by a surface voile or by a strip in the crotch region, generally made of nonwoven material, the purpose of which is to isolate the skin from the absorbent pad and which must provide a pleasant contact with the skin and the required isolation from the absorbent pad. These surface voiles or sheets and strips in the crotch region must exhibit, as essential properties, a pleasant contact with the skin, a high rate of permeation by, the body fluids, a good resistance to rewetting and must not become fluffy.
Document FR-A-2,588,285 describes a multilayer nonwoven textile which has at least two layers of nonwoven voile, one of the layers being made up of fibers of bilobar cross-section and the other layer being made up of fibers of trilobar cross-section. Each voile layer is preferably obtained by the technique of bonding when spinning (spun-bonded) and the two voile layers are joined together to form the multilayer nonwoven by heat-bonding in the compacted and noncontinuous regions.
Document WO 87/07117 describes an absorbent article of hygiene comprising an absorbent body surrounded by a cover. This surface cover or voile consists of two layers of nonwoven material. The first layer of nonwoven. material, in contact with the user""s skin, consists of a thin layer of spun-bonded fibrous fabric made of a hydrophobic material and the second layer in contact with the absorbent body is a hydrophobic fibrous layer of melt-bonded fiber fabric, similar in construction to the first layer. These two surface voile layers are not bonded together in the region intended to come into contact with the user""s body.
Document WO 88/05269 relates to a surface voile for a disposable absorbent article consisting of at least two layers of nonwoven material which can be identical or different and which are joined together by lines of adhesive forming an open pattern.
A new composite nonwoven material has also recently been developed, comprising at least one first layer consisting of a nonwoven (preferably spun-bonded) and, on this first layer, a sheet of fibers of carded type, the sheet of fibers of carded type being bonded to the base layer by needling.
Another recently developed composite nonwoven material comprises a first layer made of a nonwoven (preferably spun-bonded), a sheet of fibers of carded type and a second layer made of a nonwoven (preferably spun-bonded) of smaller weight per unit area than the first layer of nonwoven, the sheet of fibers of carded type being arranged between the first and the second layer of nonwoven, and the whole being bonded by needling.
These materials exhibit excellent body fluid pass-through times and an excellent resistance to rewetting. However, these materials have a pronounced tendency to becoming fluffy when employed as surface voile or crotch strip in absorbent articles of hygiene such as diapers.
The objective of the present invention is therefore to provide a composite nonwoven material which, when employed as surface voile or crotch strip in an absorbent article of hygiene, has an excellent rate of crossing by body fluids, an excellent resistance to rewetting and which does not become fluffy.
Another objective of the invention is to provide a process for the manufacture of such a composite nonwoven material.
Finally, an objective of the present invention is to provide an absorbent article of hygiene comprising a surface voile or a crotch region strip made of such a composite nonwoven material.
According to the present invention a composite nonwoven material is produced, characterized in that it comprises a sheet of fibers of carded type which is permeable to body fluids, comprising at least one first layer of fibers of carded type and a second layer of fibers of carded type, the fibers of the first layer having a higher denier than the fibers of the second layer, the two layers being joined together by needling.
In a recommended embodiment of the composite nonwoven material according to the invention, at least one of the layers of fibers of carded type comprises fibers chosen from fibers with a low melting point, two-component fibers and fibers mixed with a binder such as a heat-reactivable adhesive or a powder with a low melting point, and the fibers of the layers are additionally bonded by heat-melting.
In another recommended embodiment of the invention the composite material comprises, in addition to the first and second layers of fibers of carded type, a third layer made of a conventional nonwoven, permeable to fluids, for example of the spun-bonded or melt-bonded type, of low weight per unit area, bonded to one of the layers of carded type, for example the layer of fibers of carded type of lower denier.
The invention also provides a process for the manufacture of a composite nonwoven material comprising the stages consisting in:
feeding a card, in the width direction, with first fibers and second fibers, the first fibers having a higher denier than the second fibers, to form adjacent or juxtaposed strips of fibers of carded type from the first and second fibers;
supplying the adjacent strips of fibers of carded type to a lapper-spreader device to cross the strips and form a sheet consisting of superposed strips of the first and second fibers;
supplying this sheet to a sheet-stretcher device to stretch the fibers of the strips and to orient them in the direction of travel while increasing the degree of vertical orientation of said fibers in order to obtain, at the exit of the sheet-stretcher device, a sheet of fibers comprising a first layer of the first fibers and a second layer of the second fibers; and
subjecting the sheet formed to a needling from at least one of its sides.
In a recommended embodiment of the process according to the invention at least one of the layers of the sheet comprises fibers chosen from fibers with a low melting point, two-component fibers and fibers mixed with a binder such as a heat-reactivable adhesive or a powder of low melting point and the process additionally comprises the bonding together of the fibers of the layers by heat-melting, for example by reactivation using hot air passing through the sheet.
The process of the present invention can, additionally, comprise a supplementary stage consisting in bonding, for example by heat-melting, a third layer of a conventional nonwoven, of low weight per unit area, to one of the layers of fibers of carded type, for example to the layer of fibers of lower denier.
According to the present invention an absorbent article of hygiene is also produced, such as a diaper which comprises an outer layer made of material which is impervious to body fluids, an absorbent pad which is permeable to body fluids and on this absorbent pad either a surface voile or sheet, or a surface voile and a crotch region strip, the surface voile, when employed by itself, consisting of the composite nonwoven material according to the invention and the crotch region strip consisting of the composite nonwoven material according to the invention, and the surface voile of a preferably hydrophobic nonwoven, when a crotch region strip and a surface voile are employed together. In the article of hygiene the surface voile or the crotch region strip consisting of the composite material according to the invention is arranged so that the first layer of fibers of carded type of higher count is in direct contact with the internal surface of the absorbent pad and consequently the second layer of fibers of carded type of lower denier, or the third layer of conventional nonwoven either in direct contact with the user""s skin or in contact with the outer surface of the surface voile in the case where the article comprises a surface voile made of conventional nonwoven.
In a recommended embodiment the invention provides an absorbent article of hygiene such as a diaper, which comprises an outer sheet made of material which is impervious to body fluids, an absorbent pad which is permeable to body fluids, attached to the outer layer, the outer layer and the absorbent pad comprising widened opposite end parts joined by a narrower crotch region, a surface sheet, preferably hydrophobic, a crotch region strip, permeable to body fluids, arranged between the pad and the surface sheet and similar in width to the crotch region of the pad and with a length at least equal to that of the pad, this crotch region strip consisting of the composite nonwoven material according to the invention, the first layer of fibers of carded type of higher denier being directly in contact with the inner surface of the absorbent pad when the composite material according to the invention consists solely of layers of fibers of carded type, and preferably the layer made of conventional nonwoven forming the innermost layer of the crotch region strip when the composite material according to the invention additionally comprises such a layer of conventional nonwoven.
In a particularly recommended embodiment the surface sheet comprises a median lengthwise cutout forming an opening, preferably of oblong shape, and an intermediate strip, of conventional nonwoven, similar in size to that of the crotch region strip, is arranged directly on the crotch region strip, below the surface sheet.
The crotch region strip is generally bonded to the absorbent pad by any suitable means, and in particular by adhesive bonding to the edge of the absorbent pad.